The basic working principle of pyroelectric sensor:
Pyroelectric sensor is a thermoelectric infrared sensor based on the principle of thermoelectric effect. The shape of the pyroelectric infrared sensor is shown in the figure above. It can detect infrared signal from human body and convert it into electrical signal output. The rectangular window at the top of the sensor is equipped with a filter, which can make the infrared rays of 9-10 μm wavelength emitted by the human body pass through, while the infrared rays of other wavelengths are filtered out, thus improving the anti-interference ability.
Structure of pyroelectric sensor:
The pyroelectric infrared sensor consists of filter, pyroelectric detector and preamplifier. The compensated pyroelectric sensor also has temperature compensation element. The figure shows the internal structure of the pyroelectric sensor. In order to prevent the interference of the external environment to the output signal of the sensor, the above elements are vacuum sealed in a metal tube.
The filter of pyroelectric sensor is band-pass filter, which is sealed on the top of the sensor shell, so that the infrared radiation of specific wavelength can selectively pass through, and the infrared radiation reaching the pyroelectric detector + beyond its cut-off range can not pass through.
Pyroelectric detector is the core element of pyroelectric sensor. It is made by electrodepositing metal electrodes on both sides of pyroelectric crystal, which is equivalent to a flat capacitor with pyroelectric crystal as the dielectric. When it is irradiated by infrared light of unsteady intensity, the change of temperature results in the change of charge density of its surface electrode, which results in pyroelectric current.
The preamplifier consists of a source follower with high internal resistance, which converts the weak current signal of pyroelectric detector into useful voltage signal output through impedance transformation.
Application of pyroelectric sensor:
Pyroelectric materials have been widely used in many fields, such as human induction, security alarm, flame detection, harmful gas analysis and so on. In addition to the application of automatic switch and anti-theft alarm in the corridor, it has been applied in more fields. For example: the air conditioner and water dispenser that will automatically shut down when no one is in the room; the circuit that the television can judge whether no one is watching or the audience has automatically shut down after sleeping; the monitor or automatic doorbell will be automatically turned on when people are near; the camera or digital camera will automatically record the activity of animals or people, etc.